In their search for natural resources men have been directing their attention more and more to the vast ocean regions of the world. Explorations carried out in the deeper parts of the ocean have disclosed rich mineral deposits on the sea bed. Because of the extreme depth at which these deposits occur, for example, in the order of 3 or 4 miles below the ocean surface, economic mining and technologically feasible means for recovery of these mineral deposits has presented formidable problems. Large scale mining operations require use of very heavy equipment which must be lowered from a surface vessel or platform to the ocean floor. One method uses a long string of pipe lowered from a ship with the mining apparatus suspended from the lower end of the pipe. To support the heavy mining equipment a very heavy walled pipe is required. Thus, the pipe itself becomes a major factor in the total weight and very special equipment must be provided for handling the extremely heavy sections of pipe. For example, in one deep ocean mining ship, 60 foot long stands of pipe are used, each of which weighs from 30,000 to 40,000 pounds.
These heavy pieces of pipe must be handled on board a ship which is subject to pitching and rolling, as well as heave. It is essential for safety of personnel and structural integrity of the vessel and its associated equipment that the pipe be firmly constrained at all times.
In such a mining ship the pipe may be stored horizontally in special holds below deck. From there it must be brought to the deck and elevated onto a derrick platform from which it is lowered into the sea. The derrick has a travelling block that grips the upper end of a pipe and raises it towards a vertical position. As this occurs it is desirable to grip the lower end of the pipe and assure that it is brought into alignment with an existing pipe string beneath the derrick. Because of the massive weights manual labor would be unsatisfactory and a mechanism must be used for guiding and centering the lower end of the pipe. It is of some importance that damage to the exterior of the pipe is avoided. The same equipment must also move the lower end of the pipe laterally to be carried to the horizontal racker as it is removed from a pipe string.